I have two entities: parent Customer and child Order.
Each Customer has 1,000,000 Orders for example, so it is not needed in any given time to load a Customer with all Orders but I want to have this ability to make join query on these two entities in JPA.
So because of this, I must create #OneToMany relationship for making join queries.
My question is: how to get query without making joinColumn because even in Lazy mode it is possible to load 1,000,000 objects!
I just want to get query on these object with where restrictions like native join.
If you don't want the #OneToMany relationship implicitly set in your Customer class than you don't have to. You can execute JPQL queries (in very precise manner) without the marked relationship.
Assume you have:
#Entity
public class Customer {
// all Customer-related fields WITHOUT #OneToMany relationship with Order
}
#Entity
public class Order {
#ManyToOne
private Customer owner;
}
Then if you want to get all Orders for particular Customer you can execute a simple JPQL query like that:
// Customer customer = ...
// EntityManager em = ...
String jpql = "SELECT o FROM Order o WHERE o.owner = :customer";
TypedQuery<Order> query = em.createQuery(jpql, Order.class);
query.setParameter("customer", customer);
List<Order> orders = query.getResultList();
In this way you can execute the code only when you're really sure you want to fetch Customer's orders.
I hope I've understood your problem correctly.
EclipseLink has support for QueryKeys, that allow you to define fields or relationships for querying that are not mapped. Currently there in no annotation support for query keys, but you can define them using the API and a DescriptorCustomizer.
Also you do not need the OneToMany to query on it, just use the inverse ManyToOne to query,
i.e.
Select distinct c from Customer c, Order o where o.customer = c and o.item = :item
Or,
Select distinct o.customer from Order o join o.customer c where o.customer = c and o.item = :item
Related
Entity relation: Transaction(#ManyToOne - eager by default) -> Account
String sql = "SELECT new com.test.Pojo(t.account, SUM(t.value)) FROM Transaction t GROUP BY t.account";
List list = entityManager.createQuery(sql).getResultList();
By default JPA using Hibernate implementation will generate 1 + n queries. The n queries are for lazy loading of the account entities.
How can I make this query eager and load everything with a single query? The sql equivalent would be something like
SELECT account.*, SUM(t.value) FROM transactions JOIN accounts on transactions.account_id = accounts.id GROUP BY account.id
, a syntax that works well on PostgreSQL. From my findings Hibernate is generating a query that justifies the lazy loading.
SELECT account.id, SUM(t.value) FROM transactions JOIN accounts on transactions.account_id = accounts.id GROUP BY account.id
Try marking the #ManyToOne field as lazy:
#ManyToOne(fetch = FetchType.LAZY)
private Account account;
And change your query using a JOIN FETCH of the account field to generate only one query with all you need, like this:
String sql = "SELECT new com.test.Pojo(acc, SUM(t.value)) "
+ "FROM Transaction t JOIN FETCH t.account acc GROUP BY acc";
UPDATE:
Sorry, you're right, the fetch attribute of #ManyToOne is not required because in Hibernate that is the default value. The JOIN FETCH isn't working, it's causing a QueryException: "Query specified join fetching, but the owner of the fetched association was not present".
I have tried with some other approaches, the most simple one that avoids doing n + 1 queries is to remove the creation of the Pojo object from your query and process the result list, manually creating the objects:
String hql = "SELECT acc, SUM(t.value)"
+ " FROM " + Transaction.class.getName() + " t"
+ " JOIN t.account acc"
+ " GROUP BY acc";
Query query = getEntityManager().createQuery(hql);
List<Pojo> pojoList = new ArrayList<>();
List<Object[]> list = query.getResultList();
for (Object[] result : list)
pojoList.add(new Pojo((Account)result[0], (BigDecimal)result[1]));
Well PostgreSQL (And any other SQL database too) will block you from using mentioned query: you have to group by all columns of account table, not by id. That is why Hibernate generates the query, grouping by ID of the account - That is what is intended to be, and then fetching the other parts. Because it cannot predict in general way, what else will be needed to be joined and grouped(!!!), and in general this could produce situation, when multiple entities with the same ID are fetched (just create a proper query and take a look at execution plan, this will be especially significant when you have OneToMany fields in your Account entity, or any other ManyToOne part of the Account entity) that is why Hibernate behaves this way.
Also, having accounts with mentioned IDs in First level cache, will force Hibernate to pick them up from that. Or IF they are rarely modified entities, you can put them in Second level cache, and hibernate will not make query to database, but rather pick them from Second level cache.
If you need to get those from database in single hint, but not use all the goodness of Hibernate, just go to pure JPA Approach based on Native queries, like this:
#NamedNativeQuery(
name = "Pojo.groupedInfo",
query = "SELECT account.*, SUM(t.value) as sum FROM transactions JOIN accounts on transactions.account_id = accounts.id GROUP BY account.id, account.etc ...",
resultClass = Pojo.class,
resultSetMapping = "Pojo.groupedInfo")
#SqlResultSetMapping(
name = "Pojo.groupedInfo",
classes = {
#ConstructorResult(
targetClass = Pojo.class,
columns = {
#ColumnResult(name = "sum", type = BigDecimal.class),
/*
* Mappings for Account part of entity.
*/
}
)
}
)
public class Pojo implements Serializable {
private BigDecimal sum;
/* .... */
public Pojo(BigDecimal sum, ...) {}
/* .... */
}
For sure this will work for you well, unless you will use the Account, fetched by this query in other entities. This will make Hibernate "mad" - the "entity", but not fetched by Hibernate...
Interesting, the described behaviour is as if t instances are returned from the actual query and t.account association in the first argument of Pojo constructor is actually navigated on t instances when marshalling results of the query (when creating Pojo instances from the result rows of the query). I am not sure if this is a bug or intended feature for constructor expressions.
But the following form of the query should work (no t.account navigation in the constructor expression, and no join fetch without the owner of the fetched association because it does not make sense to eagerly initialize something that is not actually returned from the query):
SELECT new com.test.Pojo(acc, SUM(t.value))
FROM Transaction t JOIN t.account acc
GROUP BY acc
EDIT
Very good observation by Ilya Dyoshin about the group by clause; I completely oversaw it here. To stay in the HQL world, you could simply preload all accounts with transactions before executing the query with grouping:
SELECT acc FROM Account acc
WHERE acc.id in (SELECT t.account.id FROM Transaction t)
I have an entity which contains a list of elements and now I want to search over attributes of these elements. This constraint should be "and" connected. Please see these simple example:
#Entity
public class Parent {
#Column
#Enumerated(EnumType.STRING)
private City city;
#OneToMany(...)
private List<Children> childrens;
}
#Entity
public class Children {
#Column
#Enumerated(EnumType.STRING)
private School school;
#Column
private Integer yearInSchool;
}
Now I want to find Parents in a certain city, lets say "BigCity" with children in School "AwesomeSchool" which are in class/ year 6. I want to get the search result only via CriteriaBuilder.
So far I got:
final CriteriaBuilder c = getCriteriaBuilder();
final CriteriaQuery<Parent> query = c.createQuery(Parent.class);
final Root<Parent> r = query.from(Parent.class);
query.select(r)
.where(c.and(c.equal(r.get("city"), City.BigCity)),
c.equal(r.get("childrens").get("school"), School.AwesomeSchool),
c.equal(r.get("childrens").get("yearInSchool"), 6));
Unfortunately there are two problems here:
- it looks like I can't call get("school") on the list attribute
- this will return all parents with children which are either in "AwesomeSchool" or are 6 years in the school.
Can you help me please? I thought about using a join, but there the same question is: how can I define the where part of the join so that it considers that both attributes (school and yearInSchool) have to be fulfilled at the same time.
I found similar posts about querying for objects whose children fulfill one condition - but here the children has to fulfill two conditions at the same time.
Update 1
If I use a join to assert e.g. the "school" of one child, I get so far concerning the predicate:
Predicate predicate = r.join("childrens").get("school").in(School.AwesomeSchool)
How can I reuse this joined object to assert is also for the second filter condition?
You need to JOIN and then use the JOIN object you got when forming the join when forming the WHERE clauses.
Join childrenJoin = r.join("childrens");
query.where(c.and(c.equal(r.get("city"), City.BigCity)),
c.equal(childrenJoin.get("school"), School.AwesomeSchool),
c.equal(childrenJoin.get("yearInSchool"), 6));
Perhaps you mean your JPQL to be :
SELECT p FROM Parent p JOIN p.childrens c
WHERE p.city = :theCity AND c.school = :theSchool AND c.yearInSchool = 6
I am struggling with the JPA Criteria API for formulating a query for my data structure. Ok, my entities are as follows. I have users and groups (both share a common base class OrgEntity). Logically, users can be members in multiple groups of course. Finally, I have an entity representing a task, which has a list of potential owners (that can be either single users or whole groups). The domain model is summarized below and is given, so I cannot change it.
#Entity
#Inheritance(strategy=InheritanceType.JOINED)
abstract public class OrgEntity {
#Id
public String name;
...
}
#Entity
public class User extends OrgEntity {
public String displayName;
#ManyToMany(mappedBy="members")
public List<Group> groups;
...
}
#Entity
public class Group extends OrgEntity {
#ManyToMany
public List<User> members;
...
}
#Entity
public class Task {
#Id
public String uuid;
#ManyToMany
public List<OrgEntity> potentialOwners;
...
}
The starting point for my query is a single instance of User. I want to know all the tasks where the user is a potential owner (regardless if the user is directly contained in the potentialOwners collection or member of a group that is contained in potentialOwners).
My first attempt using a named query was as follows
SELECT DISTINCT t FROM Task AS t JOIN t.potentialOwners po
WHERE (po IN (SELECT g FROM User u JOIN u.groups g WHERE u = :user)
OR po IN (SELECT u FROM User u WHERE u = :user))
It works, but I don't know if this is the most efficient way to do this. Any suggestions?
However, I have no idea how to implement this using the criteria API. Can somebody please help me with that.
Thanks
Ok, I finally figured out how to do it. If you are interested in my solution, here it is. u is the User object, basically the query parameter and em is the EntityManager instance.
CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
// specifies the result value of the query
CriteriaQuery<Task> cq = criteriaBuilder.createQuery(Task.class);
// start with the navigation at the task entity
Root<Task> from = cq.from(Task.class);
// join the potential owner organizational entities
Join<Task,OrgEntity> potentialOwners = from.join("potentialOwners");
// select the tasks but remove duplicates
CriteriaQuery<Task> select = cq.select(from).distinct(true);
// definition for subquery1: fetch the user instance
Subquery<User> subquery1 = cq.subquery(User.class);
// start at the User entities
Root<User> from1 = subquery1.from(User.class);
// select the whole user
subquery1.select(from1);
// based on the specified user
subquery1.where(criteriaBuilder.equal(from1, u));
// definition for subquery2: fetch all groups for given user
Subquery<Group> subquery2 = cq.subquery(Group.class);
// we start at the User entity
Root<User> from2 = subquery2.from(User.class);
// join to Group entities via the groups collection
Join<User, Group> groups = from2.join("groups");
// select the group entities only
subquery2.select(groups).distinct(true);
// and finally restrict to all groups of the specified user
subquery2.where(criteriaBuilder.equal(from2, u));
// order in descending order based on the unique task id
select.orderBy(criteriaBuilder.desc(from.get("uuid")));
// here we restrict to those tasks that have the potential
// owners either in the result set of subquery2 or subquery1
// additionally I've tried to filter for another restriction
// in the task (based on a like statement of the uuid)
select.where(criteriaBuilder.and(
criteriaBuilder.or(
criteriaBuilder.in(potentialOwners).value(subquery2),
criteriaBuilder.in(potentialOwners).value(subquery1)),
criteriaBuilder.like(from.<String>get("uuid"), "1%")));
TypedQuery<Task> typedQuery = em.createQuery(select);
List<Task> resultList = typedQuery.getResultList();
I have a REST interface for a datamodel that has several one-to-many and many-to-many relationships between entities. While many-to-many relationships seem easy to manage statelessly, I'm having trouble with one-to-many. Consider the following one-to-many relationship:
Employee:
#ManyToOne
#JoinColumn(name = "Company_id")
private Company company;
Company:
#OneToMany(mappedBy = "company", cascade = CascadeType.ALL, orphanRemoval=true)
public Set<Employee> employees = new HashSet<Employee>();
When a company is updated, its employee collection may have been updated as well (employees removed or added) but since the REST interface only allows updating the company as a whole, I cannot explicitly delete or add employees.
Simply replacing the collection does not work, but I found that this seems to work:
public void setEmployees(Set<Employee> employee) {
this.employees.clear(); // magic happens here?
this.employees.addAll(employees);
for (Iterator<Employee> iterator = employees.iterator(); iterator.hasNext();) {
Employee employee = (Employee) iterator.next();
employee.setCompany(this);
}
}
Is this the way it should be done, or is there a better way?
EDIT: In fact the above does not work! It appears to work at first, but then it will break with:
Exception in thread "main" java.lang.IllegalStateException: An entity copy was already assigned to a different entity.
I assume this happens because the db already contains a set of employees and if any of the "old" employees are also part of the replacement set, they collide with the ones in the database.
So what is the right way to replace the set?
First make sure equals is implemented properly. As per hibernate spec: http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html/ch04.html#persistent-classes-equalshashcode
I had a similar problem doing a merge. Essentially I had to fetch the existing employees associated with the company. I had to merge any changes to existing employees, and then add any new employees.
Query query = em.createQuery("select e from Employee e where e.company = '" + company.getId() + "'");
Collection<Employee> existingEmployees = new LinkedList<Employee>();
try{
Iterables.addAll(existingEmployees, (Collection<Employee>) query.getResultList());
}
catch(NoResultException nre){
//No results
}
for(Employee existingEmployee : existingEmployees){
for(Employee employee : company.getEmployees()){
if(existingEmployee.name().equals(employee.name())){
employee.setId(existingEmployee.getId());
}
employee.setCompany(company);
}
}
i think you have no better choice then to replace the existing collection and simply set the new one provided by the REST response.
I have two tables: Customers and Commands, it's a #OneToMany relation from Client to Commands, one client have many Commands.
the table commands contain : idCommand, date, nameCommande, idCustomer.
the table customers contain: idCustomer, nameClient, email.
All the JPA and EJB are set up and I can easily get a list of Commands or Clients using an HQL query in a managed bean and list them in a JSP using this code.
public List<Commande> selectAllCommandes() {
List<Commande> commandes = em.createQuery("select c from Commande c").getResultList();
return commandes;
}
public List<Customer> selectAllCustomers() {
List<Customer> customers = em.createQuery("select cu from Customer cu").getResultList();
return customers;
}
How do I join the two tables with the idCustomer column in a way to show the name of client instead his id? I've used this HQL query
SELECT c.date, c.name Commande, cu.nameClient FROM Commande AS c, Customer AS cu WHERE cu.idCustomer = c.idCustomer
But I have no idea about the List<> type that I need to use to get the result/
If you map the reverse relation in the Commande entity ...
public class Commande {
...
#ManyToOne(mappedBy="commande")
private Client client;
// getter and setter ...
}
(Here, mappedBy is getting the name of the #OneToMany property set up at the
other side of the relationship)
Then after executing your query SELECT c FROM Commande c you would get a list of Commande objects, and for each one of them you could get the name of the client using: thisCommande.getClient().getName().